1. Field of the Invention
This invention relates to organic coating films which effectively absorb radiation, especially lasers of relatively long wavelengths, to convert into other energy. More particularly, it relates to a novel organic coating film suitable as: a photosensitive film for use in an electrophotographic printer which employs a semiconductor laser as a light source; an optical disc coating film which permits the writing and reproduction of information with a semiconductor laser; an infrared ray cutting filter; and so forth.
2. Description of the Prior Art
The electrophotographic printing system employing a laser as a light source reproduces a given information image by modulating the laser beam with electric signals in response to the original information image, and scanning a photosensitive surface with the modulated laser beam by means of a galvano-mirror or the like to form an electrostatic latent image, followed by toner development and transferring. Gas lasers such as a helium-cadmium laser (wavelength 441.6 nm) and a helium-neon laser (wavelength 632.8 nm) have been generally used in this printing system. The photosensitive members for these light sources are therefore satisfactory if spectral-sensitized up to around 650 nm (sensitized to operate effectively to rays of wavelengths up to around 650 nm). Such photosensitive members so far known include those (1) employing a charge transfer complex of polyvinylcarbazole with trinitrofluorenone in the photosensitive layer, (2) employing a vapor-deposited layer of tellurium sensitized with selenium as a photosensitive layer, (3) employing a photosensitive layer comprising two vapor-deposited films, one being a selenium film formed as a charge transport layer on a conductive layer and the other being a selenium-tellurium film formed on said selenium film, (4) employing cadmium sulfide, as a photosensitive layer, spectral-sensitized with a sensitizing colorant, and (5) employing two photosensitive layers functioning as a charge generation layer containing organic pigments and a charge transport layer, respectively, both spectral-sensitized up to a required longer wavelength.
The optical disc coating film can store high density information in the form of spiral or circular tracks of fine pits (e.g. about 1.mu.) optically detectable. For writing information on the disc, the surface of a laser-sensitive layer on the disc is scanned spirally or circularly with a converged laser beam modulated, thereby forming pits at the spots irradiated with pulses of the laser beam. The laser-sensitive layer can form optically detectable pits by absorbing energy of the laser. According to a heat-mode recording technique, for instance, a laser-sensitive layer absorbs thermal energy of the laser and forms small depressions (pits) by evaporation or fusing at the sites that have absorbed the thermal energy. According to another heat-mode recording technique, pits having an optically detectable density are formed at the spots which have absorbed laser energy.
The information stored on the optical disc can be read by scanning the disc surface along the track with a laser and detecting optical differences between the pits and the pit-free area. For instance, a laser is irradiated to scan the disc surface along the track and the laser energy reflected from the disc is monitored with a photodetector. When the pit-free site is irradiated, the output of the photodetector is low; when the pit is irradiated, the laser is reflected sufficiently from an underlying reflecting interface, thereby increasing the output of the photodetector.
For the recording medium to be used in this type of light, materials composed mainly of inorganic substances have been proposed until now, including thin metallic films such as aluminum vapor-deposited films, thin bismuth films, thin tellulium oxide films, and amorphous glass films of chalcogenite group compounds.
In recent years, there have been developed semiconductor laser devices of small size and low cost. Further lasers emitted from these devices can be directly modulated. However, most of these lasers have a wavelength of at least 750 nm. Accordingly, in order to carry out recording and/or reproduction with such a long-wavelength semiconductor laser, the laser-sensitive film used should have an absorption maximum in a long wavelength region generally of 750-850 nm.
However, existing laser-sensitive films, in particular those composed mainly of inorganic materials, have high reflectance for laser beams, and hence exhibit lower efficiency of laser energy utilization and poor sensitivity characteristics. In addition, extension of the response-wavelength region of these films to 750 nm or longer is disadvantageous, since these laser-sensitive films become complicated in layer construction and in particular when these sensitized films are used electrophotographic applications, the sensitizing dyes will be faded by repeated charging and exposing operations.
Such being the case, there have been proposed in recent years organic films highly sensitive to rays of wavelengths of 750 nm and longer. Examples of such organic films are those containing a pyrylium dye disclosed in U.S. Pat. No. 4,315,983 and "Research Disclosure" No. 20517 (May, 1981) and those containing a squarylium dye disclosed in J. Vac. Sci. Technol., 18 (1), 105-109 (January/February, 1981).
Besides these, a report on the photoconductivity of phthalocyanine pigments was presented in "RCA Review", Vol. 23, 413-419 (September, 1962). Electrophotographic photosensitive members employing phthalocyanine pigments were disclosed in U.S. Pat. Nos. 3,397,086 and 3,816,118. Further, disazo pigment-containing films disclosed in U.S. Pat. Nos. 3,898,084 and 4,251,613 are also known as an example of laser-sensitive organic films.
However, organic compounds having absorption maxima in the longer wavelength region are, as a rule, the more unstable, often decomposing with a slight increase in temperature. In view of these problems and additionally of various characteristics required for use in electrophotographic printers or in optical discs, organic films sensitive to long wavelength rays, hitherto proposed are not necessarily satisfactory for practical use.
These organic semiconductive materials are easy to synthesize as compared with inorganic semiconductive materials, and a compound sensitive to rays of required wavelengths can be synthesized. Electrophotographic photosensitive members having a film of such an organic semiconductive material on a conductive substrate have an advantage in better sensitivity to color. However, little organic semiconductive materials can be used with respect to sensitivity and durability in practice. Further, there have been developed in recent years organic semiconductive materials having high sensitivity characteristics to long wavelength rays of 700 nm or longer accompanying the development of low output semiconductor laser. However, there has been found no organic semiconductive material having the satisfactory characteristics.